Support multiple containers in structured format

Co-authored-by: imjasonh <210737+imjasonh@users.noreply.github.com>

container-vm/variables.tf

@@ -15,44 +15,28 @@ variable "machine_type" {
   default     = "e2-medium"
 }
 
-variable "container_image" {
-  description = "The container image to run, must be referenced by digest (e.g., 'gcr.io/my-project/my-app@sha256:abc123...')."
-  type        = string
+variable "containers" {
+  description = "A map of containers to run on the VM. Each key is the container name, and the value specifies the container configuration."
+  type = map(object({
+    image   = string
+    command = optional(string, "")
+    args    = optional(list(string), [])
+    env = optional(list(object({
+      name  = string
+      value = string
+    })), [])
+    restart_policy = optional(string, "always")
+  }))
 
   validation {
-    condition     = can(regex("^.+@sha256:[a-f0-9]{64}$", var.container_image))
-    error_message = "The container_image must be referenced by digest (e.g., 'gcr.io/my-project/my-app@sha256:<64 hex chars>')."
+    condition     = length(var.containers) > 0
+    error_message = "At least one container must be specified."
   }
-}
 
-variable "container_name" {
-  description = "The name to assign to the running Docker container."
-  type        = string
-  default     = "gce-container-app"
-}
-
-variable "restart_policy" {
-  description = "The systemd/Docker restart policy (e.g., 'always', 'on-failure', 'no')."
-  type        = string
-  default     = "always"
-}
-
-variable "container_env" {
-  description = "A map of environment variables to set in the container."
-  type        = map(string)
-  default     = {}
-}
-
-variable "container_command" {
-  description = "The optional command to override the ENTRYPOINT (e.g., '/bin/bash')."
-  type        = string
-  default     = ""
-}
-
-variable "container_args" {
-  description = "Optional arguments to pass to the container command."
-  type        = list(string)
-  default     = []
+  validation {
+    condition     = alltrue([for name, c in var.containers : can(regex("^.+@sha256:[a-f0-9]{64}$", c.image))])
+    error_message = "All container images must be referenced by digest (e.g., 'gcr.io/my-project/my-app@sha256:<64 hex chars>')."
+  }
 }
 
 variable "service_account_email" {